Digital Subscriber Line (DSL) technology is widely-used today for increasing the bandwidth of digital data transmissions over the existing telephone network infrastructure. In a typical system configuration, a plurality of DSL subscribers are connected to a service provider (SP) network through a Digital Subscriber Line Access Multiplexer (DSLAM), which concentrates and multiplexes signals at the telephone service provider location to the broader wide area network (WAN). Basically, a DSLAM takes connections from many customers or subscribers and aggregates them onto a single, high-capacity connection. The DSLAM may also provide additional functions such as Internet Protocol (IP) address assignment for the subscribers, IP Access Control Lists (ACLs), etc.
Asynchronous Transfer Mode (ATM) protocol networks have traditionally been utilized for communications between DSLAM devices and Broadband Remote Access Servers (BRAS) that provide authentication and subscriber management functions. A BRAS is a device that terminates remote users at the corporate or Internet users at the Internet service provider (ISP) network, and commonly provides firewall, authentication, and routing services for remote users. Next generation BRAS devices are frequently referred to as Broadband Network Gateway (BBNG) devices. The ATM protocol is an international standard in which multiple service types (such as voice, video, or data) are conveyed in fixed-length “cells” over point-to-point network connections. Data packet cells travel through the ATM switches from the user network interface (UNI) to the network node interface (NNI) through a process called Virtual Path Identifier/Virtual Channel Identifier (VPI/VCI) translation. The VPI/VCI identifiers are used by the ATM switches to switch/direct the subscriber traffic to a given feature server, and in the reverse direction to forward server traffic to a given DSLAM/subscriber, without ambiguity. Furthermore, the VPI/VCI mechanism is used by the feature server to identify the subscriber.
U.S. Pat. No. 6,801,533, for example, teaches a system and method for proxy signaling in a DSLAM and generally describes a DSL network that includes communication transfer of signals from a DSLAM to a remote access server over a high-speed ATM network. Transmission of packet data over an ATM network is also taught in U.S. Pat. No. 6,785,232. U.S. Pat. No. 5,818,842 teaches a communication system with an interface device that connects a plurality of interconnected ATM switches to Local Area Network (LAN) interface adapters for connection to LAN networks.
Ethernet is a technology that originated based on the idea of peers on a network sending messages in what was essentially a common wire or channel. Each peer has a globally unique key, known as the Media Access Control (MAC) address to ensure that all systems in an Ethernet have distinct addresses. Most modern Ethernet installations use Ethernet switches (i.e., “bridges”) to implement an Ethernet “cloud” or “island” that provides connectivity to the attached devices. The switch functions as an intelligent data traffic forwarder in which data packet frames are sent to ports where the destination device is attached. Examples of network switches for use in Ethernet network environments are found in U.S. Pat. Nos. 6,850,542, 6,813,268 and 6,850,521.
The use of Ethernet as a metropolitan and WAN technology has driven the need for a new set of OAM protocols. Two main areas that have been the subject of recent attention are Service OAM and Link OAM protocols. Service OAM provides monitoring and troubleshooting of end-to-end Ethernet service instances, while Link OAM allows a service provider to monitor and troubleshoot an individual Ethernet link. Much of the work on Service OAM protocols is found in the IEEE 802.1ag specification, which specifies protocols and procedures to support connectivity fault management (CFM) used for discovery and verification of the path, through bridges and LANs, taken for data frames to and from specified network users. The 802.1ag standard basically allows service providers to manage each customer service instance, or Ethernet Virtual Connection (EVC), individually. Since Service OAM typically operates on a per-EVC basis irrespective of the underlying transport mechanism, 802.1ag essentially enables the SP to determine if an EVC has failed.
Ethernet CFM, as defined in 802.1ag, relies on a functional model consisting of hierarchical maintenance or administrative domains that are defined by provisioning which switch/router ports are interior to the particular domain. In addition, maintenance end points (MEPs) are designated on the edge nodes of a domain (each EVC), and maintenance intermediate points (MIPs) are designated on relevant interior ports. FIG. 1 is an example of an Ethernet OAM network topology that illustrates a hierarchy of domains that includes customer, provider, operator, and Multi-protocol Label Switching (MPLS) domains, which correspond to Levels 0, 3, 5, and 7, respectively, in the proposed IEEE 802.1ag specification. In CFM terminology, levels define the access control structure for domain information and state, with higher numbers (toward the physical level) being bounded by lower numbers (toward the service level). As can be seen, the SP network includes an IP/MPLS core connected with a pair of Ethernet access domains via network-facing provider edge (n-PE) devices. Each access domain has a user-facing provider edge (u-PE) device providing a link with a customer edge (CE) device, which is commonly referred to as a residential gateway (RG) device. The MEPs for each domain are illustrated by a cross-hatched box under the corresponding network device, with the MIPs being shown as open boxes in the connection path.
One of the drawbacks of Ethernet CFM as defined in 802.1ag is that it presumes that every node in the network (CE-to-CE in FIG. 1) supports the full set of functionalities defined in that specification. One of these presumptions, for instance, is that every node has a MAC address. The problem, however, is that for broadband access the service terminating node at the customer premises equipment (CPE) typically does not have a MAC address or the ability to run the full protocol suite defined in the 802.1ag standard. In many cases, the first-mile connection to the customer demarcation operates in accordance with a legacy link OAM scheme such as ATM OAM, or in compliance with the IEEE 802.3 (Clause 57) standard (formerly known as 802.3ah), which do not fully support 802.1ag functionality. In other words, the ATM-only architecture of the past has evolved to the point where the DSLAM is now typically connected via ATM to the CPE and via Ethernet to the BBNG. This makes it very difficult, if not impossible, for a SP network administrator or operator to check the physical connection path that data packets take between the RG and the BBNG nodes in response to, say, a service complaint received from a subscriber with an ATM connection to a DSLAM device.
In a DSL environment, a network operator typically responds to a service complaint by executing an OAM procedure to a MEP on the DSL line based on a database that contains a mapping of a customer-id to DSLAM-name-and-port-id alongside an ATM VPI/VCI mapping for that port-id. In the proposed 802.1ag standard, each MEP is addressed by a unique MAC address (per Virtual Local Area Network (VLAN)), its Maintenance Association (MA), and a maintenance endpoint identifier “MEP-ID”. This address information, which is essential to conduct OAM functions, is commonly conveyed through the use of periodic continuity check messages (CCMs) multicast by every MEP. But in the case where there are tens of thousands of users logically connected to a single VLAN, multicasting CCMs by each MEP can result in a flood of messaging that overwhelms network resources. In addition, the BBNG terminating associated Service VLANs (S-VLANs) and Service/Customer VLAN (S/C-VLAN) combinations might have difficulty intercepting the CCMs.
One solution is to simply disable the continuous sending of CCMs by the user-line MEPs. However, this creates a new problem since those messages convey address information about a given user port, thus making it difficult to transmit a message to a target port from a remote part of the network.
Further complicating the use of 802.1ag for issuing OAM functions in an Ethernet DSL environment is the fact that many SPs consider it to be too operationally complex to maintain a database of customer-id to the MAC address assigned to each user port of the DSLAM. In other words, network SPs prefer to use a customer-id to DSLAM-name to port-id mapping, rather than retain knowledge of the MAC address of each port.
Therefore, what is a needed is a mechanism in an Ethernet DSL environment for resolving the address of a MEP situated on a given user-line, thus enabling a network operator to perform OAM functions without requiring the user-line MEP to continuously send CCMs.
By way of further background, U.S. Patent Publication No. 2005/0099951 teaches a method of detecting a fault on an Ethernet network using OAM connectivity check functions in which connectivity check frames are generated and sent to either a specific unicast destination address or a multicast destination address. United States Patent Publication No. 2005/0099949 describes a further method that defines OAM domains by defining reference points on the Ethernet network, and using the reference points to insert and extract Ethernet OAM frames. A system for interworking between a broadband system such as an ATM system and a GR-303 format system for telecommunication calls is disclosed in U.S. Pat. No. 6,667,982.